Most control systems for dual acting hydraulic or pneumatic cylinders or actuators utilize a directional control valve for controlling the flow of fluid under a constant or predefined pressure to force the actuator rod to extend or retract. In some applications, it would be desirable to not only control the direction of the fluid flow for actuating an actuator, but also to vary or regulate the fluid pressure in the fluid circuits for actuating the actuators.
One application in particular where it would be desirable to control the actuators as well as regulate or vary the fluid pressure in the fluid circuits is in connection with row cleaners on an agricultural planter. Row cleaners, such as disclosed in U.S. Pat. No. 7,673,570 (“the '570 patent”), incorporated herein in its entirety by reference, are used to clear away crop residue, soil clods and other debris that can interfere with proper furrow formation and seed growth. When planting fields with heavy crop residue, it may be desirable to exert extra downforce on the row cleaner to ensure a more aggressive action of the row cleaner to clear away the heavy crop residue. In field conditions where the crop residue is light, a less aggressive action of the row cleaner may be desired. To increase or decrease the aggressiveness of the row cleaner while on-the-go during planting operations, a hydraulic or pneumatic cylinder is typically employed to raise and lower the row cleaner. In conventional control systems for raising and lowering row cleaners equipped with a hydraulic or pneumatic actuators, the operator's only control over the row cleaners is through movement of a lever fore or aft to open and close a directional control valve in the fluid circuit thereby causing the row cleaner actuator to extend or retract to respectively lower or raise the row cleaner. Accordingly, as the planter traverses the field, the operator is required to continually look back at the row cleaners and adjust their height up or down to maintain the desired amount of aggressiveness as the soil conditions, terrain and amount of crop residue vary.
The control system disclosed in the '570 patent allows the operator to set a desired downpressure for the row cleaner which is then automatically maintained as the planter traverses the field. The '570 patent also allows the operator to change the pressure of the hydraulic fluid supplied to the cylinders. However, the pressure in the fluid circuits is controlled through an electronic control system in combination with an accumulator having a hydraulic fluid chamber and a pressurized gas chamber. Thus, while the control system of the '570 patent may serve its intended purpose it is a complex system with a higher associated cost.
It is desirable, therefore, to provide a control system which allows an operator to set a desired pressure in the fluid circuits so that as soil conditions and terrain vary during planting operations as the planter traverses the field, the actuator will self adjust to maintain the desired preset pressure in the fluid circuits. By maintaining the desired preset pressure in the fluid circuits, the row cleaner will follow the terrain or contours of the field while maintaining the desired amount of aggressiveness of the row cleaner. Furthermore, it would be desirable for such a control system to be relatively low in cost and simple to install and which is simple and intuitive to operate without the need for electronics and microprocessors.
Such a control system may have applications to other ground engaging devices on agricultural equipment or wherever there is a need for a low cost, simple and intuitive control system for providing directional control of hydraulic or pneumatic actuators over a range of variable pressures.